1. Field of the Invention
The present invention relates to a light-emitting diode (LED) device. More particularly, the present invention relates to a serial-type LED device.
2. Description of the Related Art
An LED light source employs a plurality of LEDs to provide sufficient brightness. The LEDs can be coupled in series to drive so that each LED provides substantially the same brightness due to the same current flowing through each LED. However, the serial LEDs will not work if one of the LEDs does not work. In addition, the driving voltage applied to the serial LEDs increases as the number of the LEDs coupled in series increases, so that the driving voltage may be too high, resulting result in higher cost and increasing complexity of the circuit design.
To avoid the disadvantage of the serial LEDs, the LEDs can be divided into several groups. The LEDs of each group are coupled in series as a light string, and all light strings are coupled in parallel, so that the LEDs of each light string provide substantially the same brightness and so that each light string provides the same brightness by employing a current balance technology. In addition, if one of the light strings does not work, the others of the light strings can still work. However, as the number of the light strings increases, the circuit design of the current balance circuit becomes complex.